The human eye includes a complex composition in the form of a tear film. Tears include three basic components: (1) lipids; (2) an aqueous layer; and (3) mucin. The absence of any one of these components causes discomfort and can lead to a temporary or permanent condition known as keratitis sicca (or keratoconjuctivitis sicca, often referred to as dry eye). Dry eye can have a variety of causes but is generally attributed to one or two basic malfunctions. First, the tear ducts leading from the lacrimal glands can be clogged or malfunctioning so that an insufficient amount of tears reaches the eye. For many years, this was generally thought to be the main reason for dry eye. Artificial tears were developed in response to this need. However, the relief to patients using these artificial tears is short-lived and treatment must be readministered several times each hour.
More recently, it has been discovered that, with increasing age, dry eye is caused by either insufficient or inadequate tears and tear components or the inability to maintain effective tear film. Accordingly, recent therapies have proceeded on the basis that tear production may be inadequate in some individuals and that a significant percentage of dry eye syndrome can be alleviated by slowing down the drainage of the tears through the lacrimal ducts.
Tears are removed from the eye by draining through the upper and lower punctal openings which lead into the canalicular canals (See FIG. 1). Initial attempts at sealing the puncta and/or the canalicular canals involved stitching the puncta shut or using electrical or laser cauterization to seal the puncta and or canalicular canals. Although such methodology can provide desirable results, the procedure is not reversible without reconstructive surgery. Since it is sometimes difficult to determine whether in a particular patient, the drainage is too great or the tear production is too small, irreversible blockage is not without risk.
One means of temporarily blocking the punctum and canaliculus for the treatment of dry eye is through the use of intracanalicular gelatin implants. Intracanalicular Gelatin Implants in the Treatment of Kerato-Conjunctivitis Sicca, Wallace S. Foulds, Brit J. Ophthal (1961) Vol. 45 pp 625-7. Foulds discloses that the occlusion of the lacrimal puncta can be performed by use of and insertion of a fine, water soluble gelatin rod into the punctal openings. The gelatin rod is formed from pure powdered gelatin to which a small quantity of distilled water has been added and is heated in a water bath until the gelatin dissolves and a thick gel results. By dipping a cold glass rod into the prepared gelatin, and withdrawing the same, fine solid rods of gelatin were formed. The gelatin rods were then inserted into the canaliculi to provide a temporary blockage. As such, the gelatin rod implants, although very fragile, provide an alternative means for temporarily blocking the canaliculus.
Water-insoluble plugs which can be placed in the punctum openings and into vertical sections of the canalicular canals are disclosed in U.S. Pat. No. 3,949,750, Freeman, issued Apr. 13, 1976. The punctum plug (10) of Freeman is a rod-like plug formed with an oversized tip (11) that dilates and blocks the vertical canaliculus (see FIG. 2). The punctum plug has a relatively large, smooth head portion (12) which functions to prevent the punctum plug from passing into the horizontal portion of the canaliculus. Although these plugs are reversible, they tend to become dislodged quite easily. Further, they are somewhat difficult to insert, and occasionally their size and shape can cause tissue damage during insertion or, if they protrude from the puncta, they can cause irritation to the sclera. The tissue of the punctum can also be damaged by being dilated by the plugs over extended periods of time.
An improvement on the Freeman plugs is disclosed in U.S. Pat. No. 4,959,048, Seder et al., issued Sep. 25, 1990. Seder et al. disclose a preformed plug or channel occluder which is somewhat conical in shape, making it possible to insert the occluder into the opening of the punctum more easily than the devices disclosed by Freeman. Further, Seder et al. disclose that variations in the anatomy of individuals make it desirable to provide a series of occluders in different lengths and/or widths in order to accommodate anatomical differences. Therefore, ophthalmologists need to measure the actual size of the punctal opening to determine the best size of punctum plug to be used for each patient and manufacturers must then provide five or more different sizes of punctum plugs to meet the ophthalmologist's needs.
Accordingly, using the prior art plugs, doctors must follow a number of procedures that are not only time consuming but also require a high level of skill. First, doctors need to measure each patient's punctum diameter since this size will vary from patient to patient, and for some patients, there will even be variances in punctum size in the left eye versus right eye (see FIG. 3). This is done by inserting a sizing gauge (13) into the punctum (2). An oversized plug will cause the patient discomfort while an undersized plug will fall out of the patient's eye. Second, doctors need to dilate the punctum (2) and quickly insert the plug, usually within 30 seconds or less (see FIG. 4). The dilation needs to be repeated if the plug fails to be inserted within the 30 seconds, and, since the plug is so soft and small, it is often very difficult to complete the insertion within this 30 second time window. FIGS. 4 and 5 show tools which may be used to enlarge the punctum for insertion of the plug.
From the foregoing discussion, there exists a clear need for a new punctal plug design which would greatly simplify or eliminate the current time-consuming surgical dilation and insertion procedures. A "one-size-fits-all" plug design would not only eliminate the need for manufacturers to provide doctors with plugs of various dimensions, but also eliminate the need for doctors to measure the patient's punctal size prior to surgery.